Atrial fibrillation is a common disorder and is associated with significant morbidity and mortality. New treatments for atrial fibrillation are being developed at a rapid pace, however, there is a clear lack of tools to assist the clinician in determining which treatment is best suited for a particular patient. During Phase I, we investigated a set of signal processing algorithms intended to assist in treatment of atrial fibrillation by quantifying the spatiotemporal structure of electrical propagation. We found that the algorithms not only provided a quantifiable measure of the nature of atrial fibrillation, they also allowed us to discover a new phenomena that occurs during failed defibrillation shocks. During Phase II we plan to develop a real-time version of the algorithms investigated during Phase I, and test them along with several new algorithms in the cardiac electrophysiology laboratory. Our Clinical Consultants will investigate the role of the algorithms in selecting optimal treatment regimes for patients and for guiding specific interventions including catheter ablation, cardioversion, and administration of antiarrhythmic medications. PROPOSED COMMERCIAL APPLICATION: There is intense commercial interest in development of new ways to manage the large number of patients with atrial fibrillation. Assuming that the clinical results obtained during Phase II build upon those of Phase I, we expect a significant commercial interest in the technology developed under this program. We will continue to pursue the most direct path to commercialization; licensing of this technology to existing vendors of cardiac electrophysiology workstations.